1. Field of the Invention
The present invention relates to a fuel reforming apparatus for reforming hydrocarbon-based fuel into hydrogen-rich fuel gas.
2. Description of the Related Art
In conventional fuel reforming apparatus, for example, those in JP-A-63-303801, steam is admixed into a reformed gas containing hydrogen and carbon monoxide, and the carbon monoxide in the reformed gas is converted to hydrogen and carbon dioxide by means of steam, yielding hydrogen-rich gas. Such apparatus are provided with a water-vaporizing evaporator, and the steam produced by the evaporator is admixed into the reformed gas.
The need for vaporizers makes such fuel reforming apparatus complicated and bulky. In addition, a water-vaporizing heat source is needed, and the reformed gas must be efficiently cooled before being introduced into the water gas shift reactor. These factors often reduce the thermal efficiency of the apparatus. Furthermore, conventional heat exchangers, such as those involving water, oil, or air cooling, are impaired in their ability to respond to transient variations in temperature or heat due to the heat capacity of the coolant and constituent elements used.
Accordingly, an object of the present invention is to provide a smaller, simpler, and more responsive reforming apparatus. Another object of the present invention is to render heat exchange more efficient by utilizing the latent heat generated when water is introduced into a reformed gas and vaporized, and to mix the reformed gas and vaporized steam with greater uniformity. Yet another object of the present invention is to increase the thermal efficiency of the reforming apparatus.
In order to attain at least part of the above and other related objects of the present invention, there is provided a fuel reforming apparatus for reforming hydrocarbon-based fuel into hydrogen-rich fuel gas. The fuel reforming apparatus comprises: a reforming reactor for reforming the hydrocarbon-based fuel into a reformed gas containing hydrogen and carbon monoxide; a water gas shift reactor for shifting the carbon monoxide to carbon dioxide using steam, thereby producing the carbon dioxide and hydrogen; and a water feeding/mixing unit for spraying the reformed gas with water, vaporizing the sprayed water, forming a mixture with the reformed gas, and feeding the mixed gas to the water gas shift reactor.
In the above apparatus, the water is vaporized at least partially by the sensible heat of the reformed gas because the reformed gas is directly sprayed with water. In addition, the optimal temperature of the water gas shift reactor is commonly lower than the optimal temperature of the reforming reactor, so the temperature of the mixed gas fed to the water gas shift reactor can be reduced by absorbing latent heat by the spraying and vaporization of water.
According to an aspect of the present invention, a fuel reforming apparatus comprises: a reforming reactor for generating a reformed gas containing hydrogen and carbon monoxide from the hydrocarbon-based fuel; a water gas shift reactor for reducing concentration of carbon monoxide in the reformed gas by promoting a shift reaction for generating hydrogen and carbon dioxide from carbon monoxide and steam; a water feeding unit for feeding water for use in the shift reaction into a flow path of the reformed gas; and a heat exchanger for cooling the reformed gas prior to completion of the shift reaction by exchanging heat with a coolant including water to be used in the shift reaction. The water feeding unit vaporizes the water to be used in the shift reaction that has been heated in the heat exchanger, thereby feeding the water into the flow path of the reformed gas.
In the above arrangement, the water to be used in the shift reaction that is fed to the reformed gas flow path is heated by the heat exchanger, making it possible to reduce the energy expended on vaporizing the water to be used in the shift reaction and to simplify the structure used to vaporize the water. In addition, the heat exchanger simultaneously acts to cool the reformed gas, making it possible to simplify the structure to cool the reformed gas. The entire fuel reforming apparatus can therefore be made more energy efficient.
According to another aspect of the present invention, a fuel reforming apparatus comprises: a reforming reactor for reforming the hydrocarbon-based fuel into a reformed gas containing hydrogen and carbon monoxide; a water gas shift reactor for converting steam and carbon monoxide into hydrogen and carbon dioxide; a connector for connecting the reforming reactor and the water gas shift reactor to allow the reformed gas from the reforming reactor to be fed to the water gas shift reactor, the connector including a reformed gas permeable member disposed proximate to the reforming reactor, the reformed gas permeable member having a plurality of gaps capable of passing the reformed gas from the reforming reactor; and a liquid water feeding unit for feeding liquid water to the reformed gas permeable member.
In the above arrangement, the liquid water cools the reformed gas and vaporizes by exchanging heat with the reformed gas, and is then fed to the water gas shift reactor after being mixed with the reformed gas. Supplying liquid water in an amount needed for shift reactions makes it possible to feed the steam needed for the shift reactions and to cool the reformed gas. In addition, spraying, vaporizing, and mixing liquid water in the reformed gas permeable member ensure that the heat-transfer surface is efficiently used and that the steam is uniformly admixed into the reformed gas.
According to still another aspect of the present invention, the reformed gas permeable member have a plurality of capillaries. This arrangement also makes it possible to feed the steam needed for the shift reactions and to cool the reformed gas.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.